Semiconductor devices are obtained through various fabrication operations. The fabrication operations define a plurality of features on semiconductor wafers (wafers or substrates) that span multiple levels. At the base level, plurality of transistor devices with diffusion regions is defined. In subsequent levels, interconnections using metal lines are defined and electrically connected to the underlying transistor devices resulting in semiconductor devices such as the integrated circuits (IC), memory cells, etc. Low-k dielectric materials are used to separate and insulate these features and other layers to obtain fully functional semiconductor devices. To provide better insulation between features and to further reduce coupling capacitance and power consumption, the dielectric constant of the low-k dielectric materials used is further reduced by introducing pores and by doping with chemicals such as carbon or fluorine. The resulting ultra low-k dielectric materials are good insulators, use less power, and result in reduced coupling capacitance.
During the various fabrication operations, the substrate is exposed to various contaminants. Any material or chemical used in the fabrication operations to which the substrate is exposed is a potential source of contamination. Chemicals, such as process gases, etching chemicals, deposition chemicals, etc., used in the various fabrication operations leave deposit on the surface of the substrate as particulates or polymer residue contaminants. The sizes of the particulate contaminants are in the order of the critical dimensions of the features being fabricated on the substrate. During fabrication, these contaminants lodge into hard-to-reach areas, such as in a trench surrounding delicate features. Conventional cleaning process use mechanical cleaning to clean the surface of these particulate and polymer residue contaminants. However, with technological advances leading to decreasing feature size, cleaning the surface using mechanical cleaning processes becomes quite challenging as the delicate features may get easily damaged. If the contaminants are not properly removed, the features in the vicinity of these contaminants may potentially become inoperable. Removal of such small contaminants without adversely affecting the features or the low-k material on the wafer is quite challenging.
Additionally, the ultra low-k dielectric material used in insulating features poses new challenges as the material properties, such as mechanical strength, thermal stability and adhesion to different substrate layers among others, are sometimes compromised. As the ultra low-k dielectric material is exposed to the rigors of the various fabrication operations, the dielectric material may get physically or chemically damaged by the process chemicals and/or by the fabrication processes. The damage may be due to depletion of carbon content from a portion of the ultra-low-k dielectric material immediately adjacent to the features and exposed to the process chemicals. The depletion of the carbon results in an increase of the dielectric constant in the dielectric film layer. During a stripping operation, for example, stripping plasma used to strip a carbon based photoresist layer near a feature, may damage the low-k material that is exposed to the stripping plasma by depleting the carbon from the low-k material. The carbon depletion in the low-k material results in an increase of the dielectric constant in the low-k dielectric film layer contributing to capacitive coupling. It is, therefore, essential to substantially restore the characteristics of the low-k dielectric film layer by either removing or repairing the damaged low-k dielectric film layers through which features are formed so that the functionality of the features and that of the integrated circuit devices, are preserved.
Additionally, metals have been used as conducting materials in integrated circuit production for a long time. Presently, tungsten is used at the front end to make contact with the transistors while aluminum and copper are the preferred metals for back end of the line interconnects. These metals are chemically very reactive and can react with moisture and oxygen in the ambient environment as well as other process chemicals applied to the surface leading to metal corrosion. The corrosion of metals will negatively impact the electrical integrity of the fabricated device, which necessitates metal passivation during the process flow.
It is clear from above that a most desired cleaning method should be able to perform multiple functions listed above, namely, particle removal, polymer residue removal, damaged low-k removal and repair, and metal passivation. It is in this context that embodiments of the invention arise.